Many integrated circuits now contain multiple levels of metallization for interconnections. As device geometries shrink and functional density increases, it becomes imperative to reduce the RC time constant within multi-level metallization systems. The dielectric typically used to isolate metal lines from each other is silicon dioxide. Conventional oxide etches are available for high-aspect-ratio contacts and vias. Silicon dioxide also dissipates heat effectively. However, the dielectric constant of silicon dioxide is on the order of 3.9.
Recently, attempts have been made to replace the silicon dioxide with an organic polymer having a lower dielectric constant. Inorganic compounds have also been used. A lower dielectric constant results in a reduction in the RC delay time. However, the thermal stability and etchability of organic polymers are inferior to that of silicon dioxide.